AIS Update July 2025
Underwater Footage of Middle Cullen Infestation
CLA HITTING STARRY STONEWORT INFESTATION HARD
The battle to contain the starry stonewort infestation on Middle Cullen is continuing.
On July 15, the three-acre infestation was treated for a second time with an aquatic algaecide called Komeen Descend. This relatively new product – a copper sulfate – sprays like a liquid but stays in place like a granule, which according to the manufacturer, results in longer contact time with the unwanted algae and therefore returns better results than ordinary liquid algaecides.
TIGRISS, a lake management firm based in St. Cloud, did the application. Their plan, which has been approved by the Department of Natural Resources, is to hit the infestation as hard as possible in June, July and August, and potentially September in hopes of minimizing the spread of a weedy infestation that has already doubled in size since being discovered last year.
Trying to kill and contain an invasive species algae that doesn’t want to die is not cheap. The June, July and August treatments will cost about $25,500, and if a September treatment is deemed a wise strategy by the DNR the price tag will be north of $30,000. The DNR is taking seriously the Middle Cullen infestation and is monitoring this hard-hitting approach as part of an invasive species management study.
The TIGRISS June treatment worked but “worked” is a relative term. The copper sulfate was applied, as recommended by the DNR, just as the algae was beginning to grow robustly but still far below the surface of the water. A post-treatment evaluation showed that the algae had been inhibited but nevertheless has grown to a height of about three feet and remains dense. Thankfully, the infestation is largely in water 14 to 16 feet deep so it is not coming in contact with boat props that could spread the infestation further.
It is difficult to kill starry stonewort. In fact, no infestation in the United States has ever been eradicated. This is due, in part, to the fact that starry stonewort does not have a vascular system. Unlike true plants, which have tissues that transport nutrients and water throughout the plant, starry stonewort has a very basic cellular structure. This means that when an algaecide contacts the algae the algaecide isn’t spread to roots and branchlets. Therefore, the only part of the algae that can potentially die is the part that has been in direct contact with the algaecide. As such, the taller and thicker an infestation becomes the less likely it is that the algaecide will reach its intended targets. That’s why hitting it hard right now makes sense.
Like the June treatment, the July treatment took about two hours. Applicators Matt Swanson and Brice McGowan launched their 21-foot boat at about 8:30 a.m. and were done by 10:30 a.m. Loaded onto their boat were 100 gallons of Komeen Descend, which is mixed with 100 gallons of water. The combined product is then pumped from a holding tank into two hoses that are draped over the transom on both sides of the outboard motor. The hoses are threaded through four-foot lengths of PVC pipe aimed at the bottom so the application starts at a deeper level. The goal is to introduce the chemical not too high in the water column (where it would diffuse more quickly) or too low (where it wouldn’t diffuse enough and potentially leave some areas untreated).
“We’re shooting for a cone effect,” said Swanson. “We want to get the maximum amount of product on the algae while also ensuring we don’t miss a spot. We’re using the strongest chemical formula allowed.”
Swanson and McGowan pump the algaecide into the water while monitoring an onboard digital map that shows the precise location of the infestation. Much like modern farming, they follow GPS routes to ensure they aren’t over-lapping here and missing a spot there. The chemical delivery system is calibrated to the speed of the boat so that less chemical is released when the boat slows down and more chemical is released when the boats speed up. Typically, the boat goes about two miles per hour. The infestation is located just out from the dock at the public access and slightly to the south.
The starry stonewort infestation is creating new challenges for the CLA. Typically, the CLA spends anywhere from $12,000 to $40,000 annually on curly-leaf pondweed treatments. This year, because of the additional starry stonewort treatments, the CLA’s aquatic invasive species treatment expenses will be in the $65,000 range or more. Thankfully, CLA members generously donated roughly $44,000 this year for AIS treatments. Also, the CLA sought and received about $12,000 in AIS grant funds, and another $2,500 may still be coming. Still, the potential for significant financial challenges in the future is easy to see. The need to contain the starry stonewort infestation is urgent.
Underwater video of what the starry stonewort infestation looked like in early July is available on the CLA website. Thanks again to all who contributed to the AIS fund. Your generosity is truly appreciated and needed.